In the current 3rd Generation Partnership Project (3GPP) long term evolution (LTE) time division duplex (TDD)-Advanced systems, the same frequency bands are used for the uplink and downlink transmissions between enhanced node Bs (eNodeBs) and user equipment (UE). Uplink and downlink transmissions are separated by transmitting either uplink data or downlink data at each pre-determined block of time, known as subframes, on the same frequency bands. In TDD deployment, the uplink and downlink transmissions are structured into radio frames, each 10 ms in time length. Each radio frame may comprise a single frame or two half-frames of each 5 ms in time length. Each half-frame, in turn, may comprise five subframes of 1 ms time length each. Particular designations of subframes within a radio frame for uplink or downlink transmission—referred to as uplink and downlink configurations—can be defined. The seven supported uplink and downlink configurations (also referred to UL/DL configurations, uplink-downlink configurations, or uplink-downlink ratio configurations) are shown in a table 100 of FIG. 1, in which “D” denotes a subframe reserved for downlink transmission, “U” denotes a subframe reserved for uplink transmission, and “S” denotes a special subframe which includes the downlink pilot time slot (DwPTS), guard period (GP) and uplink pilot time slot (UpPTS) fields. (See 3GPP TS 36.211 Version 10.5.0, E-UTRA Physical Channels and Modulation (Release 10), June 2012.) In the currently supported uplink-downlink configurations, between 40 to 90% of the subframes within a given radio frame are downlink subframes.
The evolved universal terrestrial radio access network (EUTRAN) decides which one of the supported uplink-downlink configurations applies for a given cell in the network with the underlying assumption that all cells within the network change the TDD UL/DL configuration synchronously. Once the uplink-downlink configuration has been allocated, this configuration is typically not changed during normal operation of the cell or cells served by the enhanced Node B (eNodeB). This is the case even when uplink or downlink transmission loads are mismatched to the current uplink-downlink configuration. Even if the uplink-downlink configuration for a given eNodeB is desirous of being changed, there is a minimum latency of 640 ms under the current standard to effect modification of the System Information Block 1 (SIB1) information—the mechanism by which the uplink-downlink configuration is allocated and re-allocated. Current 3GPP LTE-Advanced systems do not support dynamic adjustment of the uplink and downlink ratio configurations.
Even when the LTE system is capable of dynamic adjustment of the uplink and downlink ratio configurations, care should be taken to ensure that such feature does not introduce network inefficiencies or degrade signal quality as a result of the impact from inter-cell DL-UL interference that may potentially negate the benefits of adapting the UL/DL configurations to match possibly different traffic conditions in respective cells.